Attention is a fundamental property of cognitive architecture. Abnormalities of attention characterize a wide variety of clinical disorders and diseases, such as autism and Parkinson's disease. Changes in attention also characterize the normal aging process, as well as the response to a variety of drugs. Attention is also important in understanding the effects of sleep deprivation, including effects on medical personnel. A proper understanding of attention is central to understanding a range of public health problems. Our long term goal is to understand how people perform attention demanding everyday tasks. Consider driving. Driving requires attention to be focused over a period of minutes or hours, rather than milliseconds. Driving requires attention to multiple moving objects. While we may be driving continually for minutes to hours, we often need to shift attention among various subtasks (e.g. reading signs or dashboard instruments) without losing track of other cars on the road. However, our current understanding of attention has been largely built on studying brief or static displays. We cannot understand complicated behaviors like driving by studying processing of brief snapshots. Our everyday environment and behaviors are dynamic and extended in both time and space. In order to understand attention, therefore, we must study attention under similar conditions. We call this the study of dynamic attention. We propose to study three fundamental problems in dynamic attention. First, we will study the nature of capacity limitations in dynamic attention. Second, we propose a new theory, derived from the concept of association fields in contour perception, to explain how the visual system predicts object trajectories. Finally, we will study the mechanisms underlying successful multitasking. We propose to address these issues using both behavioral and electrophysiological approaches. Behavioral methods will be built on the multiple object tracking task. Additionally, we will use event-related potential methods to develop a neurophysiological index of tracking. We will employ this index to study questions which cannot be answered by purely behavioral methods. Relevance: Attention is a fundamental property of the brain. Impairments in attention underlie a wide variety of public health issues, from autism and attention deficit disorder to the aging process and the effects of sleep deprivation. We propose to study how attention works in complex, dynamic environments, using a combination of cognitive and neuroscience approaches.